In the fermentation industry, cell culture media is typically formulated to provide all nutrients necessary for the growth of a host cell line, with particular emphasis on meeting the cell line's requirements for carbon, nitrogen, phosphorus, sulfur, and other major nutrients. Some cell lines require additional components, including amino acids, trace minerals and metals, and complex growth factors. The presence of these nutrients provides a suitable growth environment for the organism of choice and, unfortunately, for any potential contaminating organisms. In this environment the production organism is required to compete directly with any contaminant organism in the cell culture.
Even in robust hosts, the combination of opportunistic infections of the culture and the metabolic burden resulting from the demands of product manufacture is a major concern in monoculture operations. Industrial robustness is typically considered a multigenic trait specific to the host strain and thus difficult to engineer predictably into organisms late in the development process. Addition of selective growth inhibitors, such as bacterial antibiotics, is one method used to create a more robust fermentation environment for host organisms that are resistant to the growth inhibitor. However, antibiotic addition is often undesirable or unfeasible, and spontaneously resistant contaminations frequently result.
Accordingly, there exists a need for rationally engineered traits that, when engineered into a host organism, create a robust monoculture fermentation environment.